Pulp fibers are used in the manufacture of many absorbent components for absorbent articles including, for example, diapers, feminine products, adult incontinence products, and paper products. The pulp fibers used to produce these products are supplied as rolled pulp or bale pulp. Rolled pulp is generally a continuous roll of a type of pulp known as fluff pulp. In comparison, bale pulp generally consists of a stack of individual pulp sheets. Two primary methods exist to process bale pulp and rolled pulp to obtain the individual fibers generally required to manufacture fibrous products. One method is an air-laid process where a defiberizer, such as a hammermill, interacts with the pulp to separate the individual fibers of the individual sheet or roll of pulp. The defiberizer exposes the fibers in the pulp while avoiding clumping and other adverse conditions that may cause apparent defects in an end product. The separate fibers are suspended in air and subsequently transferred to a forming surface such that an embryonic absorbent component is formed. The other method used to produce absorbent components is a wet-laid process. In a wet-laid process, pulp, typically in the form of individual sheets of pulp, is supplied to a device where the pulp is mixed with an aqueous solution to form a fibrous slurry. The fibrous slurry is then deposited onto a forming wire or belt such that an absorbent component is formed.
Sheet pulp or fluff pulp may be used in both an air-laid process and a wet-laid process. In air-laid processes, fluff pulp or rolled pulp has been the primary choice among manufacturers. Fluff pulp is the preferred material in air-laid processes because of its structural characteristics, such as a lower moisture content and more uniform density. In addition, fluff pulp is supplied in roll form allowing for a continuous strip of pulp to be fed into the defiberizer without creating any interruption in the defiberizing process. An interruption is characterized by a break or inconsistency in laying down fibers on a forming surface. Avoiding an interruption is important to the quality of products produced by the process. For the above reasons, manufacturers using an air-laid process generally choose rolled pulp to produce fibrous products.
Further to the above, manufactures have usually avoided using bale pulp in air-laid processes because of interruptions in the defiberizing process. When dealing with short, individual sheets of pulp, it is often the case that one sheet of pulp is pulled into the defiberizer at a faster rate than a subsequent sheet of pulp can be fed into the defiberizer. This gap in feeding sheets of pulp into the defiberizer can create an interruption in the supply of individual fibers to a forming surface. The resulting interruption in the defiberization process ultimately may result in an inconsistent, varied product. Such an interruption in the production of an absorbent component for an absorbent article could result in a product having inadequate absorbency or inferior softness.
Sheet pulp and rolled pulp are generally made of the same raw material. Despite this similarity, individual sheets of pulp offer some advantages over rolled pulp. Sheet pulp is less expensive than rolled pulp and can be transported and stored more easily than rolled pulp. The cost difference between rolled pulp and bale pulp is due in part to the process used to produce bale pulp, which is a less expensive process than that used to produce rolled pulp. In addition, bale pulp is produced by a large number of sources and, therefore, offers manufacturers more choice in suppliers and the ability to localize supply with the point of demand. In comparison, fluff pulp is a specialized grade of pulp that is produced by an expensive processes requiring large costly machinery. The expense of the equipment itself coupled with the expense to operate the equipment has resulted in relatively few suppliers of fluff pulp. As a result, fluff pulp represents a small percentage of the overall pulp market. Therefore, sheet pulp offers economic benefits over fluff pulp.
Due to the benefits of using bale pulp, processes for defiberizing individual sheets of pulp have been developed to try to combat the problem of fiber interruption. For example, defiberizers have been developed for accepting numerous unattached sheets of pulp that have been laid against of one another; that is numerous sheets of pulp in shingled relation enter the defiberizer at one time. Another apparatus has been developed to defiberize a pulp sheet with two defiberizing mechanisms in angled relation so that the force exerted on the pulp sheet is not parallel to the machine direction, and the feed of the pulp sheet can be controlled more easily. Still another apparatus that has been developed shreds the sheets of pulp and stores the shredded pulp in a hopper to create a uniform supply of shredded pulp for defiberization. Another method involves folding the sheets of pulp, where the fold line is parallel to the machine direction, to create a sheet of uniform thickness to be fed into the defiberizer. Generally, the above-discussed processes keep the sheets of pulp essentially separate from one another, which could still result in an interruption of fibers. In other words, the individual sheets of pulp in the existing processes are not attached to one another.
Accordingly, there is a need for a process that is capable of transforming individual sheets of pulp into a strip of pulp that simulates a continuous roll of pulp being fed into a defiberizer to form an absorbent component.